1. Field of the Invention
The present invention relates generally to a fluid-filled vibration damping device for use in an automotive engine mount or the like, for example, and more particularly, to techniques capable of providing an effective and simple solution for noises caused by cavitation generated in association with input of impact load or the like.
2. Description of the Related Art
Conventionally, as one type of vibration damping devices such as vibration damping connectors or vibration damping supports configured to be interposed between components that make up a vibration transmission system, there have been known fluid-filled vibration damping devices that utilize vibration damping effect on the basis of flow action of the fluid filling the interior. Such fluid-filled vibration damping devices, as disclosed in Japanese Unexamined Patent Publication No. JP-A-2005-337348 for example, have a structure including a primary fluid chamber which gives rise to pressure fluctuations based on deformation of a main rubber elastic body at times of vibration input, an auxiliary fluid chamber which gives rise to pressure differentials relative to the primary fluid chamber at times of vibration input, and an orifice passage which permits communication between the two chambers. With this arrangement, vibration damping effect will be exhibited on the basis of flow action of a non-compressible sealed fluid which is induced to flow through the orifice passage between the primary fluid chamber and the auxiliary fluid chamber which give rise to pressure differentials relative to each other at times of vibration input.
Meanwhile, with such a fluid-filled vibration damping device, noises or vibrations generated at input of impact load may sometimes be a problem. These noises etc. are attributed to cavitation bubbles generated by a sudden drop of pressure in the primary fluid chamber due to the input of impact load.
To address this problem, as disclosed in U.S. Pat. No. 7,306,210, proposed is a structure which includes a short-circuit passage equipped with a relief valve or the like between the primary fluid chamber and the auxiliary fluid chamber so as to rapidly dispel the excessive negative pressure within the primary fluid chamber.
However, since this structure requires the relief valve, the short-circuit passage, or the like specially, there is a problem that an increased number of components or a complicated construction are inevitable.
Also, U.S. Publication No. US2011/0155887 discloses techniques in order to minimize cavitation by adding a small amount of liquid having a high vapor pressure (a low boiling point), such as silicone oil or the like, into the sealed fluid such as ethylene glycol or the like.
However, since the liquid having a high vapor pressure boils under the environment of relatively low temperature, there is a problem that the environment suitable for using the vibration damping device is limited. In particular, it is never desirable to employ the vibration damping device as a vibration damping device for automobiles which have an internal combustion engine and many of which are used in direct sunlight. Thus, implementation in an automotive engine mount, for example, is difficult because the engine compartment is likely to heat up.